1. Field of the Invention
The present invention relates to a semiconductor laser device incorporating a semiconductor laser element using a group III nitride semiconductor.
2. Description of Related Art
In general, group III nitride semiconductors of the formula InxGayAlzN (where x+y+z=1, 0≦x≦1, 0≦y≦1, and 0≦z≦1) have large energy band gaps and high thermal stability, and their band gap widths can be controlled through adjustment of their composition. For these reasons, group III nitride semiconductors have been researched for application in various semiconductor devices such as light-emitting elements and high-temperature devices. In the field of light-emitting elements, there have already been put into practical use light-emitting diodes (LEDs) that offer luminous intensity of the order of several candelas in a blue to green region of the spectrum. Also in the field of laser diodes (LDs), researches are being made steadily for commercialization.
With respect to LDs, there have conventionally been developed devices that use an insulating substrate made of a material that is comparatively readily available, such as sapphire. Recently, however, with a view to resolve lattice mismatching between a substrate and an epitaxial layer, to reduce defects, to obtain good cristallinity, and out of other considerations, devices using a GaN substrate have been developed increasingly eagerly. For example, Japanese Patent Application Laid-Open No. H11-312841 discloses a nitride semiconductor laser element using a GaN substrate.
The substrate of a semiconductor laser element needs to have low defect density. For this reason, according to one conventionally proposed technique, defects are concentrated in a particular region (the dislocation-concentrated region) within the substrate, and a laser waveguide is formed on the remaining region (the low-dislocation region). This permits laser operation to take place in a region with fewer defects, and thus helps prolong the useful life of the element. However, a problem arises when a semiconductor laser element using such a substrate undergoes a wire-bonding process in which wires of Au or Al are bonded thereto through which to permit a drive electric current to be fed thereto, because this process has been found to cause a new deterioration in the element.